The invention relates to a module, particularly a steering-wheel module, that unifies three functional groups, namely an energy-transmission device, an information-transmission device and an angle-sensor mechanism, in a compact, two-part component.
The basic model of inductive position or angle sensors according to the transformer principle comprises at least two conductor loops, one of which is operated as a transmitter or primary coil, while the other serves as a receiver or secondary coil. If the secondary coil is guided past the primary coil, a secondary voltage that is dependent on the position of the primary coil relative to the secondary coil is obtained in the transformer formed by the primary coil and the secondary coil with variable coupling. Special embodiments of these sensors operate with short-circuited secondary coils. In these sensors, the angle-dependent feedback of the short-circuited secondary coil to the primary coil is measured. The very low resistance of the secondary winding that is present with a short-circuit manifests itself in the primary circuit as a transformer ratio for resistances that is modified by the variable mutual inductance. The company of Hella KG Hueck and Co. distributes an accelerator-pedal sensor for use in motor vehicles, which is described, for example, in the ATZ Automobiltechnische Zeitschrift [Automotive Technology Journal] 100 (1998), No. 10.
It is therefore the object of the invention to expand the function of an angle sensor operating according to the inductive principle to include energy transmission and information transmission. It is a further object of the invention to propose a steering-wheel module that combines the three functional groups of an energy-transmission device, an information-transmission device and an angle-sensor mechanism into a compact, multi-part, inexpensive component.
In accordance with the invention, these objects are accomplished by the characterizing features of the independent claims. The dependent claims disclose further advantageous embodiments.
A module that, in accordance with the invention, includes an angle-sensor mechanism, an energy-transmission device and an information-transmission device comprises at least two circuit boards. One circuit board forms the stator with respect to the angle-sensor mechanism, while the other forms the rotor with respect to the mechanism. The stator includes the primary coil for the angle-sensor mechanism, as well as an exciting coil for the transmission of energy and information. The rotor includes the secondary coil of the angle-sensor mechanism, as well as a receiver coil for the transmission of energy and information. The exciting coil and the receiver coil are disposed in circular fashion on the respective circuit board, thereby creating a coupling for the exciting coil and receiver coil that is independent of the angle. The exciting coil and the receiver coil are used for transmitting both energy and information. The energy transmission is typically effected with a medium frequency of, for example, 25 kHz. A modulation is superposed on this medium frequency for transmitting information. Various modulation methods are feasible, such as HF (high-frequency) modulation, amplitude modulation or phase modulation.
A module in accordance with the invention, which integrates the angle-sensor mechanism, the energy-transmission device and the information-transmission device, offers the following advantages in connection with the use of modern construction and connection technology:
The structural size of the module can be kept small at the transmitted powers of up to about 10 W; in particular, ferrite cores are not required for focusing the magnetic flux.
The module is expandable, and the information-transmission system permits a large number of additional functions.
The module operates in contactless fashion, and is therefore unsusceptible to wear. In particular, the module requires no sliding contacts.
The module is durable.
The module can be produced with circuit-board technology, and is therefore suitable for mass production, which makes it inexpensive to produce.
The module according to the invention is advantageously specially adapted to the requirements of the respective installation site. In the configuration of the module as an integrated steering-wheel module in a motor vehicle, the circuit-board technology advantageously allows the module to be adapted to different vehicles, such as trucks having 24-V on-board networks, passenger vehicles having 42 V on-board. networks or passenger vehicles having 12 V on-board networks. Other motor vehicles with different types of on-board networks are also conceivable. The stator-side part of the steering-wheel module is permanently built into the motor vehicle, e.g., secured to the chassis of the vehicle, or secured to the steering-shaft jacket tube. The rotor-side part of the steering-wheel module must be mounted in the immediate vicinity of the stator. If the stator-side part of the steering-wheel module is secured to the steering-shaft jacket tube, the rotor-side part of the steering-wheel module is secured to the steering shaft, so the rotor-side part of the steering-wheel module can be rotated relative to the stator-side part of the module.
In an advantageous embodiment of the module according to the invention, the primary and secondary coils of the angle-sensor mechanism, and the exciting coils and the receiver coils of the energy- and information-transmission devices, are embodied as conductor tracks on the surface of the circuit boards. In an especially preferred embodiment, the primary coil, secondary coil, exciting coil and receiver coil are embodied as a printed circuit. This technology has performed well for angle-sensor mechanisms, that is, for the primary and secondary coils. Surprisingly, preliminary tests of the invention have shown that, for the purpose of transmitting power and information, that is, for the exciting and receiver coils, powers of up to, for example, 10 Watts can be transmitted without difficulty with coils produced with circuit-board technology, or with printed-circuit coils. This is all the more surprising because, contrary to popular belief, ferrite cores that focus on the magnetic field can be omitted in the power transmission. A power of about 1 to 2 Watts is typically required for deploying an airbag built into the steering wheel, for example. The power that can be transmitted with printed circuits is therefore sufficient for reliably igniting a vehicle airbag with the integrated steering-wheel module. Supplying energy to driver""s-side airbags is an especially preferred application of the module according to the invention.
In a further preferred embodiment, the supply systems for the angle-sensor mechanism and the energy- and information-transmission devices are already integrated onto the circuit boards of the module according to the invention. In this case, so-called DC/AC converters, current transformers for converting direct current into alternating current, are provided on the stator side of the circuit boards, while AC/DC converters are integrated on the rotor side. Digital modulators/demodulators are integrated on both the stator and rotor sides for transmitting information. In a preferred embodiment, the modulators/demodulators are capable of transmitting a plurality of transmission channels. In a preferred embodiment, five channels can be transmitted, for example; in a further embodiment, ten channels can be transmitted, for example, while in another embodiment, 30 channels can be transmitted, for example. The number of channels depends on the number of connected devices that must be supplied with information independently of one another, or that must supply information independently of one another. An especially preferred application of the module according to the invention, in addition to the aforementioned supply of energy to driver""s-side airbags, is the transmission of control commands from actuation elements integrated into the steering wheel to the associated devices, such as switches for controlling and operating car radios or CD (compact disc) players.